Vapor generating and superheating operation



Jan. 20, 1959 -w. L. PAULISON, JR 7 2,869,520

VAPOR GENERATING AND SUPERHEATING OPERATION I Filed Aug. 24. 1953 5Sheets-Sheet l COND.

' BURNERS AIR HEATER FIG. I

INVENTOR.

WILLIAM L. PAULISON JR.

Jan. 20, 1959 W. L. PAULISON, JR

VAPOR GENERATING AND SUPERHEATING OPERATION 5 Sheets-Sheet 2 Filed Aug.24, 1953 3 r m 5 4 a 5 #1.!- P 0 MY .W, WWW, m 5 MH Mn fl mw u m Ci k 1w T k i M 2 q m w T J 1 mm w 4 w lwflm w n m Q Q 3 M A k g: if Q M VREHEATER SUPERHEATER BY-PASS INVENTOR. WILLIAM L. PAULISON JR.

ATTORN FIG. 2

Jan. 20, 1959 w. L. PAULISON, JR 2,869,520

VAPOR GENERATING AND SUFERHEATING OPERATION Filed Aug. 24, 1953 5Sheets-Sheet 5 Jan. 20, 1959 Filed Aug. 24, 1953 STEAM TEMPERATURE F w.L. PAULISON, JR 2,869,520

VAPOR GENERATING AND SUPERHEATING OPERATION 5 Sheets-Sheet 4 CONVECTIONCHARACTERISTICS O (UNCONTROL.LED)(|)(2)(3) l 50 SUPERHEAT fig REH AT a iE i BALANCED SH-RH O00 DESIRED FTT 65 |0o% LOAD I RH DAMPERS OPEN -T SHDAMPERS z 2 J a) ,Q 4 E BY-PASS DAMPERS I UJ 1 CLOSED O BOILER LOADINVENTOR. 5 WILLIAM L. PAULISON JR. FIG. B

ATTO EY Jan. 20, 1959 w. L. PAULISON. JR

VAPOR GENERATING AND SUPERHEATING OPERATION I Filed Aug. 24, 1955 I 5Sheets-Sfiaet 5 m;m L L m m I m w EH A 4/ D 8 PE A/ m L w A B I a s m. ym; & M. M M T A TU H H D I M S H Rm E R L G R mm T mm m ,7 I m m 9 O m:Re I D ww m a L m 5 o O C m m m w FIG. 6

VAPDR GENERATING AND SUPERHEATING OPERATION William L. Paulison, Jr.,Ridgewood, N. 1., assignor to Bailey Meter Company, a corporation ofDelaware Application August 24, 1953, Serial No. 375,963

Claims. (Cl. 122479) My invention lies in the field of steam powergeneration and particularly in the control of steam temperature inconnection with present day vapor generators. I am particularlyconcerned with the problems encountered in units rated at 1,000,000 to1,500,000 lb. per hr., operating at pressures from 1500 p. s. i. g. to2000 p. s. i. g., and with final total steam temperatures of the order1000 to I050 F. Modern units of this type may have reheat provisions,taking steam exhausted from a high pressure turbine at say 600-800 p. s.i. g. and reheating this steam to a range of l0001050 F. The problemsinvolved in the generation and close control of the properties of steamin such a unit are quite different now than was the case at the time ofthe inventions in this field which are shown in the prior art.

Superheat temperature control is particularly desirable in thegeneration of steam for the production of electrical energy in largecentral station power plants. In such plants, the upper limit ofsuperheat temperature is governed by the materials and construction ofthe turbines served by the steam. In the interest of turbine efliciencythe temperature of the steam delivered to the turbine should bemaintained within close optimum limits throughout a wide range ofoperation.

I contemplate a unit wherein the furnace chamber is surrounded by wallsof closely spaced bare tubes constituting the vapor generating sectionprimarily radiantly heated. The superheating and reheating portions ofthe vapor flow path are preferably located beyond the gas outlet of thefurnace in what is termed convection heating locations and, in theparticular embodiment which I will describe, the superheating andreheating portions of the flow path are located in separate and parallelgas flow paths with distribution dampers for regulating the distributionof heating gases between the two vapor paths. I For any given furnace,as load increases, the rate of heat absorption does not increase asrapidly as the rate of heat liberation; therefore, the furnace leavingtemperature will rise. With both the quantity rate and the temperatureof the gases leaving the furnace increasing with load, it is apparentthat a fixed surface convection superheater will receive a greater heatrate at higher loads than at lower loads and the heat transfer area isusually designed for receiving the volume and temperature of leavinggases at an expected rated load. Any further increase in the heatrelease rate supplies to the fixed superheater surface more heat by gasvolume and by gas temperature than it is designed for and acorresponding excessive final steam temperature is experienced. On theother hand, at operation below the rated load, the fixed superheatersurface receives less volume and lower temperature gases leaving thefurnace with a corresponding lowering of final steam temperature.

Inasmuch as the pressure and heat content per 1b. of the low pressuresteam returned to the reheater from the high pressure turbine exhaustdecreases with reduction in load, while the pressure and heat contentper lb. of the high pressure steam introduced to the superheater remainsvted States Patent 0 C? 2,869,520 Patented Jan. 20,1959

substantially constant with a corresponding variation in load, thecustomary installation of convection superheater and reheater will givea steam temperature-load graph which will slope downward from maximumload to low load, with the result that de.ivery temperatures from boththe superheater and reheater will droop, and the outlet temperature-loadgraph for the reheater will have a greater slope than the correspondinggraph of the superheater. This is clearly shown in Figs. 5 and 6.

The unit is preferably designed so that the final total temperature ofthe superheated steam and of the reheated steam will equal or exceedthat which is desired through the expected operating range and, in thepresent embodiment, I contemplate that this should be in a range of65-l00% of capacity. In other words,'the surfaces and passages will beso designed that the uncontrolled characteristic of each 'of thesurfaces crosses the optimum final temperature line on the graph atapproximately 65% of capacity and lies above the optimum temperaturevalue at all ratings from 65% to capacity. It is to be understood thatoperation below this design point will produce superheated steam andreheated steam at a final total temperature lower than the optimum andcontinued low-load operation is not expected.

Due to the uncontrolled characteristic, operation in the range (65100%rating) will find the final total temperature of the superheated steamand of the reheated steam greater than that which is desired withpossible danger to the turbine, and it becomes necessary to prevent thesteam from reaching the excessive temperature throughout this rangeofoperation. Preferably, I accomplish this through by-passing some ofthe heating gases around the convection heating surfaces when operatingthrough the range 65100% rating.

Due to the difference in slope of the characteristic curve of thesuperheater and of the reheater it is seen that the two finaltemperatures may depart from equality or from desired relationship ofvalues and this I correct by proportioning the total heating gasesbetween the superheating and reheating convection surfaces.

In general then, I have provided a method and apparatus for maintainingoptimum final temperature of the superheated steam and of the reheatedsteam for some arbitrary range of operation, as for example 65100%rating, through the agency of gas proportioning over the parallelsuperheating and reheating surfaces and, where necessary, by-passingsome of the heating gases around both of the superheating surfaces.

When, hereafter, I use the term throttled with reference to the postion,or positioning, of a damper, I intend to mean that the damper is in someposition between closed and open. If a damper is closed it istheoretically shutting off all flow of gases therethrough. If it is openthen it theoretically allows flow of gases therethrough unimpeded by thedamper. At any intermediate damper position the gas flow is throttled orimpeded as to its free flow and, while it may be more strictly correctto speak of the gas flow as being throttled in different degree atdifferent damper positions, it is not incorrect to say that the damperis throttled or in a throttling position. When the damper is moved in anopening direction or in a closing direction it is still in a throttingposition so long as it is not closed or open.

To reach the desired high superheated steam temperature, but not toexceed it, requires careful proportioning of the heat absorbing surfacesboth for generating steam and for superheating it. But even if thedesired superheated steam temperature be just attained initially by verycareful designing at some rated load, the superheated temperature willvary during operation by reason of changes in cleanliness of the heatabsorbing surfaces.

Slag will form and adhere to the heat absorbing surfaces in. the furnacethereby reducing the effectiveness of such surfaces and raising thefurnace outlet temperature of the products of combustion. Furnace outlettemperature will also change with percentage of excess air supplied forcombustion, with the characteristics of the fuel burned, and with therate of combustion and the corresponding rate of steam generation. Allof these things will therefore affect the temperature of the gases,whether the superheating e ements are located in series or in parallelpaths. In other words the theoretical characteristic curves are forideal designed conditions of operation and, while the general trend ofthe curve is followed, with rating. the actual final temperature of thesuperheated steam or of the reheated steam may be above or below thetheoretical curve or the optimum value at any time, for differentreasons and at different rates of operation. By the method and apparatusof my invention I tend at all times to return final total superheatedsteam temperature and final total reheated steam temperature towardoptimum value, upon departure therefrom, regardless of the cause of suchdeparture, through an operating range arbitrarily chosen in the presentembodiment as 65-100% of capacity.

In the drawings:

Fig. 1 is a somewhat diagrammatic sectional elevation of a steamgenerating and superheating unit of the type contemplated, havingconvection superheating and reheating surfaces located in parallel gasflow paths, and with a gas flow by-pass.

Fig. 2 diagrammatically represents a pneumatic control system for theunit of Fig. 1.

Fig. 3 is a modification of the control system of Fig. 2.

Fig. 4 illustrates a manual control station for regulating the operationof the unit of Fig. 1.

Figs. 5 and 6 are graphs of characteristics of convection superheatingand reheating surfaces of a unit like Fig. 1.

Fig. 7 shows a modification of Fig. 2.

Referring now to Fig. l I show therein in quite diagrammatic form, andnot to scale, a vapor generating and superheating unit in connectionwith which I will explain my invention. The furnace 1 of the unit issupplied with fuel and air for combustion through burners 2 (notdetailed). Gaseous products of combustion leave the furnace aftercontacting the fluid heating surfaces thereof. The generator is of theradiant type, wherein the furnace 1 has walls 3 of vertical, closelyspaced plain tubes constituting the vapor generating portion of theunit. Products of combustion pass upwardly through the furnace 1 in thedirection of the arrow, through a tube screen 4, over a secondarysuperheating surface 5 and a secondary reheating surface 6, to theentrance of three parallel gas passages SH, BP and RH. In the SH path islocated the primary superheating surface 7, while ,in the RH path islocated the primary reheat surface 8.

dampers 9, while that through the RH path is regulated by thepositioning of dampers 10. by-pass is regulated by dampers 11.

Considering now the vapor flow path, it will be seen that saturatedsteam from the separation drum enters Flow through the :a header 12,passes upwardly through superheating surface 7 and through a conduit 13to the secondary superheater 5. The superheated steam then leaves theunit through a conduit 14 to a high pressure turbine 15, exhaustingthrough a conduit 16 to a header 17 entrance to the'reheating surface 8.From the reheater the steam passes through a conduit 18 to thesecondary'reheater 6 from which it passes by way of a conduit 19to a lowpressure turbine 20 exhausting to a condenser. This, in simplifieddiagrammatic fashion, is the vapor cycle of .the system; Pressure of thesuperheated steam in conduit 14 is determined by-a -Bourdon tubedevice21 While final total temperature S HT of the steam is measured by adevice 22. The weight rate of flow of superheated steam through theconduit 14 to the high pressure turbine 15 is continuously measured by ameter 23. In the reheated steam conduit 19 the pressure is determined bya Bourdon tube 24 While its final temperature RHT is determined by themeasuring device 25.

My present invention contemplates both a method and apparatus foroperating and controlling the operation of avapor generating andsuperheating unit of the type described, through the positioning ofdampers 9, 10, and 11 in accordance with, or responsive to, measurementsof variables such as pressure, temperature, or flow of the superheatedsteam, and pressure, or temperature of the reheated steam. I furthermorecontemplate using air flow as a load index, under certain conditions ofdesign or operation, and while such an air flow meter is not shown inFig. 1, it will be appreciated that the air flow meter would provide acontinuous determination of either the fresh air supplied for combustionto the burners of the unit, or of the total products of combustionpassing through the unit. In speaking of air flow, I intend to mean theproducts of combustion and excess air as an indication of rating, andthis may well be measured in known fashion by taking the pressure dropacross a selected portion of the gas passages of the unit. On the otherhand, it may be true air flow by being a measure of rate of flow of airsupplied to promote combustion as measured in the duct supplying theburners.

Referring now to Fig. 2 I illustrate therein, in quite diagrammaticfashion, a pneumatic control system for continuously and automaticallyregulating the final total temperature of the superheated steam and ofthe reheated steam in connection with units such as that of Fig. 1. At30 I designate a recorder controller for the superheated steamtemperature 81-11 and for the reheated steam temperature RHT. Apneumatic pilot valve 31 may be of a known type as disclosed in theJohnson Patent 2,054,464 establishing in a pipe 32 a fluid loadingpressure continuously representative of final total temperature of thesuperheated steam supplied to the turbine 15. In similar fashion a pilotvalve 33 establishes in a pipe 34 a fluid loading pressure continuouslyrepresentative of the final total temperature of the reheated steampassing to the low pressure turbine 20 through conduit 19. The pipe 32communicates with the A chamber of a relay 35 while the pipe 34communicates with the B chamber of the relay.

Relay 35 is a differential standardizing relay of the type described andclaimed in the Dickey Patent 2,098,913 and provides an output pressurein a pipe 36 from the D chamber of the relay. Such a relay provides aproportional control with reset characteristics from a comparison of, ordifferential between, the value of SHT and RHT. It provides for thedifferential or discrepancy between these two final total temperatures afloating control of high sensitivity superimposed upon a positioningcontrol of relatively low sensitivity. A function of the adjustablebleed connection 37 between the D and C chambers is to supplement theprimary control of the pressure developed in pipe 36, as representativeof the differential between the pressures in pipes 32, 34, with asecondary control of the same or of a different magnitude as a follow-uor supplemental action to prevent overtrave! and hunting.

The output of relay 35, in pipe 36, is available to a manual-automaticselector station 38 which is preferably of the type disclosed in thepatent to Fitch 2202,48). The selector station 38 provides thepossibility of remote manual, or automatic, control of the SH dampers 9and the RH dampers 10, together but in reverse direction, by virtue of areversing relay 39. The output fluid loading pressure from station 38,available in a pipe 40, is subjected upon the B chamber of reversingrelay 39 and directly uponthe A. chamber of calibrating relay 41.

' motive means 45 for positioning the dampers 9. The

output of the relay 41, effective in a pipe 46, acts through a selectorstation 47 upon the motive means 48 for positioning the reheat dampers10. Thus a signal, in the pipe 40, calling for a change in theproportioning of the gas flow over the superheating and reheatingsurfaces, will act upon both devices 45, 48 but in reverse direction.

The air flow meter 5t positions the movable element of a pilot 51establishing in a pipe 52 a fluid loading pressure continuouslyrepresentative of the load index air flow. The pipe 52 joins the Achamber of a relay 53 whose C chamber is joined by a pipe 54 subjectingupon the C chamber a fluid loading pressure established in accordancewith the total of the final superheated steam temperature and the finalreheated steam temperature.

A branch of pipe 32 joins the A chamber of a totalizing relay 55 whilepipe 34 joins the C chamber of the relay, the two fluid pressures actingin the same direction to totalize and the relay 55 produces in a pipe 56a fluid load ing pressure continuously representative of such total.Pipe 56 joins the A chamber of a relay 57 which may be a simple relay,or a standardizing relay, according to the action of the solenoid valve58 in the bleed connection between the D and C chambers of the relay.Solenoid valve 58 is connected by cable 59 with contacts 608 of themeter 3 and the contacts 60B are closed at and above the optimum finaltemperature SHT of the superheated steam. Thus, when a rating ofapproximately 65% is reached, as indicated by final superheat steamtemperature reaching optimum value, the solenoid valve 58 opens thebleed connection between chambers D and C whereby the relay 57 providesa standardizing action between the pressure in pipe 56 and that in 54leading to the C chamber of relay 53.

Fig. 7 shows a possible modification of Fig. 2 wherein the valve 58,connecting the C and D chambers of relay 57, is bellows actuatedresponsive to loading pressure in pipe 56 and thus is sensitive to total(Fig. 2) or average (Fig. 3) of the SHT and RHT values; rather than toone only of the temperatures.

The output of relay 53, available in a pipe 60, controls the positioningof motive means 62, through a manualautomatic selector station 61, andthus the position of dampers 11. At the same time the control fluidpressure in pipe 60 joins a calibrating relay 63 whose output, availablein a pipe 64, joins the B chamber of each of relays 41, 42.

In the present embodiment it is desired to have the final superheattemperature and the final reheat temperature both at 1000" F. In certaininstallations it might be desirable to have the final temperaturesdifferent the one from the other, as for example, the final SHT 1050 F.while the final RHT 1000" F. This would be accomplished by a constantbias in the controls wherein they would, in effect, control to the sametemperature standard but one would be biased somewhat relative to theother. It is proposed to manipulate the superheat and reheat dampers insequence to equalize the two temperatures (or in predetermined relationto each other) and control the by-pass to maintain the correct value ofthe total or average temperatures. It the by-pass damper is wide openand the temperatures are still too high then the superheat and reheatdampers may be somewhat throttled to force more gas through the wideopen by-pass. In general the operation of the SH and RH dampers is insequence with the bypass dampers. However, it is a matter of selectivityrather than true sequence, and the proper combination of damperthrottling will be automatically accomplished by the system of Fig. 2 tocontinually attempt to maintain each of the final temperatures at thedesired value throughout a preselected range of operation, in this case,from 65100% of rating.

The over-all operation of the system of Fig. 2 is as follows, referencebeing had to Figs. 5 and 6. The load index controller (air flow 50)begins to open the bypass damper 11 as the boiler load increases aboveapproximately 65%, by transmitting the loading pressure in pipe 52,through the averaging relay 53, pipe 60, and selector station 61, to themotive means 62. This gradual opening of the by-pass damper, inaccordance with load increase, is shown in the lower portion of thegraph Fig. 5; the RH dampers and SH dampers being open. Throughout theoperating range (GS-%) tne by-pass damper opening is modified asrequired by the sum or the SHT and RHT controller loading pressures(corresponding to 2000 F.) transmitted from the totalizing relay 55 tothe averaging relay 53 by way of pipe 56, standardizing relay 57, andpipe 54. It being understood that throughout this range, as previouslymentioned, solenoid valve 58 is open thus allowing a regulated bleedbetween the D and C chambers of relay 57 making it a standardizing typeof relay.

Should the sum of the two temperatures start to in crease above 2000 F.with a wide open by-pass damper, both the SHT and RHT dampers will bethrottled together to force the required add.tional gas through theby-pass section. This action is accomplished by an increase in controlloading pressure transmitted from pipe 60, through the calibrating relay63 and pipe 64 and applied to the two calibrating relays 41, 42. Thus,control from boiler load as modified by the sum of the two steamtemperatures, will tend to maintain the sum of the two temperaturesconstant (at 2000 F.) above approximately 65% boiler load.

At boiler loads below 65% the sum of the SHT and RHT temperatures,indicated by the value of the loading pressure in pipe 56, is relayeddirectly through simple relay 57 and pipe 54, to the C chamber of relay53. The loading pressure in pipe 54 will, under these conditions,

never exceed a predetermined value corresponding to the totaltemperature of 2000 F. to be attained at approximately 65% boiler load.When the summation temperature of 2000 F. is reached, at approximately65% boiler load, not only would the loading pressure of pipe 54,effective in the C chamber of relay 53, tend to exceed the predeterminedvalue, but the contact 60B Will close, thus opening the bleed 58 betweenthe C and D chambers of relay 57, turning it into a standardizing actionso that any further increase in the summation of the SHT and RHTtemperatures will cause a regenerative amplification of the controlpressure in pipe 54 until the condition has been corrected by theby-pass damper and the SH and RH dampers. As previously mentioned, theby-pass damper first opens gradually until it is wide open and, if thishas not satisfied, or returned the total temperature to a value of 2000F., then the signal in pipe 60, acting through the relay 63 and pipe 64,is effective upon both relays 41 and 42 to cause both of the SH and RHdampers to be throttled downward thus forcing more gas through theby-pass.

Referring to the lower portion of the graph in Fig. 5 it will beobserved that I have shown the SH dampers and RH dampers throttled inparallel from the load where the by-pass damper is wide open. This is asequential operation which is accomplished by the system beingdescribed. On the other hand, it is possible that there may be someoverlap and that actually the SH and RH dampers will begin to bethrottled together slightly before the by-pass damper is wide open.

When the SHT control pressure (in pipe 32), and the RHT control pressure(in pipe 34), are equal, and the standardizing relay 35 into which theircontrol pressures terminate is balanced, an increase in reheated steamtemperature above superheated steam temperature transmits a change inoutput of the standardizing relay 35 through the pipes 36, 40 in adirection that throttles the 7 reheat control dampers 9. If the SHdamper is Wide open itwould not move. If it is not wide open it mighttend to open while the RH damper tends to close. A decrease in reheatedsteam temperature below superheated steam temperature reverses the dire,.on of the differential standardizing relay output go and causes thereheat damper to tend to open while the superheat damper tends to close.Should the re ater steam temperature remain lower than the sutemperature, the differential standardizing put would continue to changein the same :1 and cause the superheater damper to throttle (leaving there heat damper wide open) as required to equalize the =nperatures. Theoutput of the difierentlal s relay 35 is applied to the SH and dan rodrives through selector valves, reversing and can't; relays asindicated. Thus, the superheat and re dampers are positioned to maintainequal superb rated and reheated steam temperatures. At boiler load nerethe sum of these two temperatures of 2000" F. is available each will becontrolled at 1000 F.

Referring to the lower portion of the Fig. 5 will be understood thatthis is d'agrammatic in SH and RH dampers may not start to close ratingshown or the by-pass dampers becom at the rating shown. The three setsof dam all moving at the same time but in proper direction to satisfythe desideratum of op superheated steam temperature and optima. rcheatedsteam temperature at whatever boiler load is had between 65% and 100%.It will be appreciated that, while certain sequential or selectiveactions between the control mechanisms and the damp tors, this goes onsimultaneously and continuously upon any departure of the two finaltemperatures from their desired value. The actual positioning of thedampers is one of precedence where the pro" is operated in the properdirection so t shift of gas flow between the three parallel paths is theright direction to cause the final steam temperature to approach thedesired values.

In the upper portion of the Fig. 5 gr ph have indicated a normal designwherein the uncontrolled convection characteristic (1) for thesuperheating surface is substantially similar to the uncontrolledconvection c acteristic (2) for the reheat surface except that the lfalls off somewhat more rapidly upon decrease in For a design wherethese curves are spaced in sub tial parallelism, the balance or averageof final temperature value at 65% boiler load. su design, throughout thecontrol range 65lG" be: the total of SHT and RHT m :hi well be 261?? F.

the reheat temperature and call for the reach. gas flows over the reheatand superheat surfi.

explained.

Fig. 6 shows how these graphs might loo-l: if the dcsign were such thatthe uncontrolled convection characteristics actually crossed exactly onhe desired temperature 1000" F. at 65% bo'ler rating. in tnis conditionthe reheat curve would tend to be above curve for the range (SS-100%rating and the 4.

relative to the. other, that both the high pressure and reheat steamwill be at exactly 950 F. even though the total of the two is only 1900"F.

Under certain conditions it may be desirable that one a or the oi-rer ofthe SH and RH dampers will always be wlile the other dampers areadjusted to throttle T is is to prevent the possibility of both .13drifting toward their closed position.

of Figs. 5 and 6 do not show this neverability of such sequentialoperation exists )ll of the various relays and other devices Under thisparticular adjustment either the or the SH dampers are throttlcd whilethe -aintained in a wide open position although, temperature is abovethat which is desired ..ctor enters into the system to tend to throttle1 RH and SH dampers and force some of the heat over the by-pass.Provisions may be sup- .f d a ainst the possibility of both dampers everreachi ed position by remotely actuated pneumatic SLi l mit the damperthrottling, unless under in; uation through the selector stations.

D the lower graphs of Figs. 5 and 6 it is not t ale to show theinter-action of all three sets of all loads, both above and below 65%.For simplicity I have shown the SH and RH n to a loft-d where theby-pass dampers are upon an increase in load). From what has con said,however, it will be apparent that below 65%, either, or both, the SH maybe throttled to equalize the SH aturcs regardless of whether the totalor the average 1000 F. This is not plot because it may be that the SHdamper with the RH damper open, or the RH damper 'lli SH damper open, orboth tbrottled in 3 show a portion only of the system of Fig.

g therefrom in that the load index in this instance is superheat steamilo v rate measured at 23 (Pig. ll and the contacts 613A are actuated atapproximately '65 31? of 1g rather than from the attainment of pre- "eed temperature value as was the case in Fig. 2. the relay 55A isindicated as an averaging than as a totalizing relay.

. l have schematically illustrated certain inrecording instrumentalitiesuseful as a guide remote control of the variable operating facaerationsof the unit in accordance with in the conduit 1 leading to the highpressure 5 and provides a visual indication thereof on The indicatingdevices 22, 25 provide mani- 1.nal superheated steam temperature andsteam ter oerature respectively. The air controller 5t] and thesuperheated steam controller 23 provided not only a visual but permanentcontinuous record of these The points of measurement of these opmay bewidely scattered but I prefer- :neters at a central control locationhaving station Preferably the panelboard each-board type wherein theindicating struments are mounted on the vertical are below.

Upon the bench-board portion of the panel 1 indicate threeForward-Revsrse-Stop push button stations 101 actively controlling.electric motors 45A, 48A and l for rem to manual positioning of thedampers 9, iii, 11.

it will now be clear that my improved methods of oreration of the unitmay be manually performed by 75 an operator located at the Station 100,observing the measuring instrumentalities, and selectively remotelyactivating the motors 45A, 48A and 62A for positioning the dampers 9,10, ll. Selective and sequential operation may be obtained, as well asproper proportioning of the gases over the superheater and reheater,with or without, the bypass in service.

It is understood in this art that either vapor out-fio rate or air flowrate may be used as an index of output or boiler rating.

While I have chosen to illustrate and describe certain preferredembodiments of my invention, it will be appreciated that the inventionmay be embodied in other forms, and thus I do not desire to be limitedto the specific showings disclosed.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is:

1. Apparatus for controlling the operation of a vapor generating andsuperheating unit of the type having a convection vapor superheater anda convection vapor reheater disposed respectively in divided andseparate parallel structurally defined gas flow passages from a commoncombustion space and having a controllable structurally defined gasby-pass around the said parallel heating passages, including incombination, damper throttling means for the superheater passage, damperthrottling means for the reheater passage, damper throttling means forthe by-pass, means continuously determining reheat final totaltemperature, means continuously determining reheat final totaltemperature, means continuously ascertaining an index of load upon theunit, first control means responsive to both the superheat final totaltemperature and the reheat final total temperature determining means andproducing a control etfect representai0 tive of the total of the twotemperatures, means arranged to position the by-pass damper meansconjointly responsive to said first control means and said load indexmeans, a second control means responsive to both the superheat finaltotal temperature and the reheat final total temperature determiningmeans and producing a second control effect representative of thediiference of the two temperatures, and means selectively responsive tosaid second control efiect arranged to throttle the damper of thesuperheat passage or of the reheat passage whichever temperature ishigher while leaving the opposite damper open.

2. The combination of claim 1 including limiting means makingineffective the by-pass damper positioning means for opening saidby-pass from closed condition when either the load index is below apredetermined value or the total of the two temperatures is below apredetermined value.

3. The combination of claim 1 wherein the control effect produced bysaid first control means is representative of the average of the twotemperatures.

4. The combination of claim 1 including means responsive to the loadindex ascertaining means also effective upon the selective means.

5. The combination of claim 1 wherein the control efiects are fluidpressures.

References Cited in the file of this patent UNITED STATES PATENTS2,298,700 Junkins Oct. 13, 1942 2,519,240 Fellows Aug. 15, 19502,526,843 Birchler et a1. Oct. 14, 1950 2,649,079 Van Brunt Aug. 18,1953 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.2,869,520 January 20, 1959 William L Paulison, Jr

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 2', line '70, after "heated" insert ,steem column 8,

line 58, for "provided" read mprovide column 9, line 28, for "reheat"read me super-heat i Signed and sealed this: 8th day of September 1959.i

Attest:

; KARL H AXLINE ROBERT C. WATSON Attesting Officer Commissioner ofPatents

